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Microphones exploit the motion of suspended membranes to detect sound waves. Since the microphone performance can be improved by reducing the thickness and mass of its sensing membrane, graphene-based microphones are expected to outperform state-of-the-art microelectromechanical (MEMS) microphones and allow further miniaturization of the device. Here, we present a laser vibrometry study of the acoustic response of suspended multilayer graphene membranes for microphone applications. We address performance parameters relevant for acoustic sensing, including mechanical sensitivity, limit of detection and nonlinear distortion, and discuss the trade-offs and limitations in the design of graphene microphones. We demonstrate superior mechanical sensitivities of the graphene membranes, reaching more than 2 orders of magnitude higher compliances than commercial MEMS devices, and report a limit of detection as low as 15 dBSPL, which is 10-15 dB lower than that featured by current MEMS microphones.

Creating a good contact between electrodes and graphene nanoribbons (GNRs) has been a long-standing challenge in searching for the next GNR-based nanoelectronics. This quest requires the controlled fabrication of sub-20 nm metallic gaps, a clean GNR transfer minimizing damage and organic contamination during the device fabrication, as well as work function matching to minimize the contact resistance. Here, we transfer 9-atom-wide armchair-edged GNRs (9-AGNRs) grown on Au(111)/mica substrates to pre-patterned platinum electrodes, yielding polymer-free 9-AGNR field-effect transistor devices. Our devices have a resistance in the range of 106-108 Ω in the low-bias regime, which is 2-4 orders of magnitude lower than previous reports. Density functional theory calculations combined with the non-equilibrium Green's function method explain the observed p-type electrical characteristics and further demonstrate that platinum gives strong coupling and higher transmission in comparison to other materials, such as graphene., Applied Physics Letters, 122 (17), ISSN:0003-6951, ISSN:1077-3118

The possibility to study quantum interference phenomena at ambient conditions is an appealing feature of molecular electronics. By connecting two porphyrins in a cofacial cyclophane, we create an attractive platform for mechanically controlling electric transport through the intramolecular extent of π-orbital overlap of the porphyrins facing each other and through the angle of xanthene bridges with regard to the porphyrin planes. We analyze theoretically the evolution of molecular configurations in the pulling process and the corresponding changes in electric conduction by combining density functional theory (DFT) with Landauer scattering theory of phase-coherent elastic transport. Predicted conductances during the stretching process show order of magnitude variations caused by two robust destructive quantum interference features that span through the whole electronic gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). Mechanically-controlled break junction (MCBJ) experiments at room temperature verify the mechanosensitive response of the molecular junctions. During the continuous stretching of the molecule, they show conductance variations of up to 1.5 orders of magnitude over single breaking events. Uncommon triple-and quadruple-frequency responses are observed in periodic electrode modulation experiments with amplitudes of up to 10 Å. This further confirms the theoretically predicted double transmission dips caused by the spatial and energetic rearrangement of molecular orbitals, with contributions from both through-space and through-bond transport. This journal is

The Kagome lattice is an important fundamental structure in condensed matter physics for investigating the interplay of electron correlation, topology, and frustrated magnetism. Recent work on Kagome metals in the AV3Sb5 (A = K, Rb, and Cs) family has shown a multitude of correlation-driven distortions, including symmetry breaking charge density waves and nematic superconductivity at low temperatures. Here, we study the new Kagome metal Yb0.5Co3Ge3 and find a temperature-dependent kink in the resistivity that is highly similar to the AV3Sb5 behavior and is commensurate with an in-plane structural distortion of the Co Kagome lattice along with a doubling of the c-axis. The symmetry is lower below the transition temperature, with a breaking the in-plane mirror planes and C6 rotation, while gaining a screw axis along the c-direction. At very low temperatures, anisotropic negative magnetoresistance is observed, which may be related to anisotropic magnetism. This raises questions about the types of the distortions in Kagome nets and their resulting physical properties including superconductivity and magnetism.

Suspended piezoelectric thin films are key elements enabling high-frequency filtering in telecommunication devices. To meet the requirements of next-generation electronics, it is essential to reduce device thickness for reaching higher resonance frequencies. Here, the high-quality mechanical and electrical properties of graphene electrodes are combined with the strong piezoelectric performance of the free-standing complex oxide, BaTiO3 (BTO), to create ultrathin piezoelectric resonators. It is demonstrated that the device can be brought into mechanical resonance by piezoelectric actuation. By sweeping the DC bias voltage on the top graphene electrode, the BTO membrane is switched between the two poled ferroelectric states. Remarkably, ferroelectric hysteresis is also observed in the resonance frequency, magnitude and Q-factor of the first membrane mode. In the bulk acoustic mode, the device vibrates at 233 GHz. This work demonstrates the potential of combining van der Waals materials with complex oxides for next-generation electronics, which not only opens up opportunities for increasing filter frequencies, but also enables reconfiguration by poling, via ferroelectric memory effect.

Alkanes serve an important role as benchmark system in molecular electronics. However, a large variation in the conductance values is reported in the literature. To better understand these fluctuations, in this study we measure large molecular data sets (up to 100 000 breaking traces) of a series of alkanes with different lengths and anchoring groups using the mechanically controlled break junction (MCBJ) technique. Employing an unsupervised learning algorithm, we investigate both the time evolution and the distance dependence of the measured traces. For all the molecules considered, we have been able to identify the single-molecule conductance value for the fully stretched molecular configuration. For alkanedithiols, the corresponding extracted β decay constant of 1.05 ± 0.08 per CH2group agrees well with literature values. In the case of the stronger thiol bonding, additional peaks in the conductance histograms are found, suggesting the formation of molecular junctions containing a single molecule plus additional gold/molecule unit(s). The results shine light on the dispersion in reported conductance values and show that the evolution of the molecule as a function of stretching and time contains crucial information in determining the molecular junction configuration in MCBJs.

Biological electron transport is classically thought to occur over nanometre distances, yet recent studies suggest that electrical currents can run along centimetre-long cable bacteria. The phenomenon remains elusive, however, as currents have not been directly measured, nor have the conductive structures been identified. Here we demonstrate that cable bacteria conduct electrons over centimetre distances via highly conductive fibres embedded in the cell envelope. Direct electrode measurements reveal nanoampere currents in intact filaments up to 10.1 mm long (>2000 adjacent cells). A network of parallel periplasmic fibres displays a high conductivity (up to 79 S cm−1), explaining currents measured through intact filaments. Conductance rapidly declines upon exposure to air, but remains stable under vacuum, demonstrating that charge transfer is electronic rather than ionic. Our finding of a biological structure that efficiently guides electrical currents over long distances greatly expands the paradigm of biological charge transport and could enable new bio-electronic applications., Cable bacteria’ form long multicellular filaments that can transfer electrical currents over centimetre-long distances. Here, Meysman et al. show that the electrical currents run along highly conductive fibres embedded in the cell envelope, and charge transfer is electronic rather than ionic.

Strain engineering is one of the most effective approaches to manipulate the physical state of materials, control their electronic properties, and enable crucial functionalities. Because of their rich phase diagrams arising from competing ground states, quantum materials are an ideal playground for on-demand material control, and can be used to develop emergent technologies, such as adaptive electronics or neuromorphic computing. It was recently suggested that complex oxides could bring unprecedented functionalities to the field of nanomechanics, but the possibility of precisely controlling the stress state of materials is so far lacking. Here we demonstrate the wide and reversible manipulation of the stress state of single-crystal WO3 by strain engineering controlled by catalytic hydrogenation. Progressive incorporation of hydrogen in freestanding ultra-thin structures determines large variations of their mechanical resonance frequencies and induces static deformation. Our results demonstrate hydrogen doping as a new paradigm to reversibly manipulate the mechanical properties of nanodevices based on materials control., 6 pages, 4 figures, 9 supplementary sections

Quantum interference (QI) of electron waves passing through a single-molecule junction provides a powerful means to influence its electrical properties. Here, we investigate the correlation between substitution pattern, conductance, and mechanosensitivity in [2.2]paracyclophane (PCP)-based molecular wires in a mechanically controlled break junction experiment. The effect of themetaversusparaconnectivity in both the central PCP core and the phenyl ring connecting the terminal anchoring group is studied. We find that themeta-phenyl-anchored PCP yields such low conductance levels that molecular features cannot be resolved; in the case ofpara-phenyl-coupled anchoring, however, large variations in conductance values for modulations of the electrode separation occur for the pseudo-para-coupled PCP core, while this mechanosensitivity is absent for the pseudo-meta-PCP core. The experimental findings are interpreted in terms of QI effects between molecular frontier orbitals by theoretical calculations based on density functional theory and the Landauer formalism.

Nano letters 21(18), 7617-7624 (2021). doi:10.1021/acs.nanolett.1c02237, Published by ACS Publ., Washington, DC

The dynamics of suspended two-dimensional (2D) materials has received increasing attention during the last decade, yielding new techniques to study and interpret the physics that governs the motion of atomically thin layers. This has led to insights into the role of thermodynamic and nonlinear effects as well as the mechanisms that govern dissipation and stiffness in these resonators. In this review, we present the current state-of-the-art in the experimental study of the dynamics of 2D membranes. The focus will be both on the experimental measurement techniques and on the interpretation of the physical phenomena exhibited by atomically thin membranes in the linear and nonlinear regimes. We will show that resonant 2D membranes have emerged both as sensitive probes of condensed matter physics in ultrathin layers, and as sensitive elements to monitor small external forces or other changes in the environment. New directions for utilizing suspended 2D membranes for material characterization, thermal transport, and gas interactions will be discussed and we conclude by outlining the challenges and opportunities in this upcoming field., Comment: 39 pages, 16 figures

Theoretical studies suggest that mastering the thermocurrent through single molecules can lead to thermoelectric energy harvesters with unprecedentedly high efficiencies.1,2,3,4,5,6This can be achieved by engineering molecule length,7optimizing the tunnel coupling strength of molecules via chemical anchor groups8or by creating localized states in the backbone with resulting quantum interference features.4Empirical verification of these predictions, however, faces considerable experimental challenges and is still awaited. Here we use a novel measurement protocol that simultaneously probes the conductance and thermocurrent flow as a function of bias voltage and gate voltage. We find that the resulting thermocurrent is strongly asymmetric with respect to the gate voltage, with evidence of molecular excited states in the thermocurrent Coulomb diamond maps. These features can be reproduced by a rate-equation model only if it accounts for both the vibrational coupling and the electronic degeneracies, thus giving direct insight into the interplay of electronic and vibrational degrees of freedom, and the role of spin entropy in single molecules. Overall these results show that thermocurrent measurements can be used as a spectroscopic tool to access molecule-specific quantum transport phenomena.

Single molecules are nanoscale thermodynamic systems with few degrees of freedom. Thus, the knowledge of their entropy can reveal the presence of microscopic electron transfer dynamics that are difficult to observe otherwise. Here, we apply thermocurrent spectroscopy to directly measure the entropy of a single free radical molecule in a magnetic field. Our results allow us to uncover the presence of a singlet to triplet transition in one of the redox states of the molecule, not detected by conventional charge transport measurements. This highlights the power of thermoelectric measurements which can be used to determine the difference in configurational entropy between the redox states of a nanoscale system involved in conductance without any prior assumptions about its structure or microscopic dynamics.

Paper has the potential to dramatically reduce the cost of electronic components. In fact, paper is 10 000 times cheaper than crystalline silicon, motivating the research to integrate electronic materials on paper substrates. Among the different electronic materials, van der Waals materials are attracting the interest of the scientific community working on paper-based electronics because of the combination of high electrical performance and mechanical flexibility. Up to now, different methods have been developed to pattern conducting, semiconducting and insulating van der Waals materials on paper but the integration of superconductors remains elusive. Here, the deposition of NbSe2, an illustrative van der Waals superconductor, on standard copy paper is demonstrated. The deposited NbSe2 films on paper display superconducting properties (e.g. observation of Meissner effect and resistance drop to zero-resistance state when cooled down below its critical temperature) similar to those of bulk NbSe2., Paper has the potential to dramatically reduce the cost of electronic components but the integration of electronic materials is challenging. Here the integration of NbSe2, a van der Waals superconductor, on paper is demonstrated.

Paper holds the promise to replace silicon substrates in applications like internet of things or disposable electronics that require ultra-low-cost electronic components and an environmentally friendly electronic waste management. In the last years, spurred by the abovementioned properties of paper as a substrate and the exceptional electronic, mechanical and optical properties of van der Waals (vdW) materials, many research groups have worked towards the integration of vdW materials-based devices on paper. Recently, a method to deposit a continuous film of densely packed interconnects of vdW materials on paper by simply rubbing the vdW crystals against the rough surface of paper has been presented. This method utilizes the weak interlayer vdW interactions and allows cleaving of the crystals into micro platelets through the abrasion against the paper. Here, we aim to illustrate the general character and the potential of this technique by fabricating films of 39 different vdW materials (including superconductors, semi-metals, semiconductors, and insulators) on standard copier paper. We have thoroughly characterized their optical properties showing their high optical quality: one can easily resolve the absorption band edge of semiconducting vdW materials and even the excitonic features present in some vdW materials with high exciton binding energy. We also measured the electrical resistivity for several vdW materials films on paper finding exceptionally low values, which are in some cases, orders of magnitude lower than those reported for analogous films produced by inkjet printing. We finally demonstrate the fabrication of field-effect devices with vdW materials on paper using the paper substrate as an ionic gate., Comment: 4 figures in main text, 21 figures in Supp. Info

Ultrafast optical control of magnetic anisotropy in a van der Waals antiferromagnet activates a sub-THz two-dimensional magnon., Van der Waals magnets provide an ideal playground to explore the fundamentals of low-dimensional magnetism and open opportunities for ultrathin spin-processing devices. The Mermin-Wagner theorem dictates that as in reduced dimensions isotropic spin interactions cannot retain long-range correlations, the long-range spin order is stabilized by magnetic anisotropy. Here, using ultrashort pulses of light, we control magnetic anisotropy in the two-dimensional van der Waals antiferromagnet NiPS3. Tuning the photon energy in resonance with an orbital transition between crystal field split levels of the nickel ions, we demonstrate the selective activation of a subterahertz magnon mode with markedly two-dimensional behavior. The pump polarization control of the magnon amplitude confirms that the activation is governed by the photoinduced magnetic anisotropy axis emerging in response to photoexcitation of ground state electrons to states with a lower orbital symmetry. Our results establish pumping of orbital resonances as a promising route for manipulating magnetic order in low-dimensional (anti)ferromagnets.

The appealing feature of molecular electronics is the possibility of exploiting functionality built within a single molecule. This functionality can be employed, for example, for sensing or switching purposes. Thus, ideally, the associated conductance changes should be sizable upon application of external stimuli. Here, we show that a molecular spring can be mechanically compressed or elongated to tune its conductance by up to an order of magnitude by controlling the quantum interference between electronic pathways. Oscillations in the conductance occur when the stress built up in the molecule is high enough to allow the anchoring groups to move along the surface in a stick-slip-like fashion. The mechanical control of quantum interference effects and the resulting large change in molecular conductance open the door for applications in, e.g., a minute mechanosensitive sensing device functional at room temperature., 23 pages, 6 figures

In the field of nanomechanics, parametric excitations are of interest since they can greatly enhance sensing capabilities and eliminate cross-talk. Above a certain threshold of the parametric pump, the mechanical resonator can be brought into parametric resonance. Here we demonstrate parametric resonance of suspended single-layer graphene membranes by an efficient opto-thermal drive that modulates the intrinsic spring constant. With a large amplitude of the optical drive, a record number of 14 mechanical modes can be brought into parametric resonance by modulating a single parameter: the pre-tension. A detailed analysis of the parametric resonance allows us to study nonlinear dynamics and the loss tangent of graphene resonators. It is found that nonlinear damping, of the van der Pol type, is essential to describe the high amplitude parametric resonance response in atomically thin membranes.

Owing to their atomic-scale thickness, the resonances of two-dimensional (2D) material membranes show signatures of nonlinearities at forces of only a few picoNewtons. Although the linear dynamics of membranes is well understood, the exact relation between the nonlinear response and the resonator’s material properties has remained elusive. Here we show a method for determining the Young’s modulus of suspended 2D material membranes from their nonlinear dynamic response. To demonstrate the method, we perform measurements on graphene and MoS2 nanodrums electrostatically driven into the nonlinear regime at multiple driving forces. We show that a set of frequency response curves can be fitted using only the cubic spring constant as a fit parameter, which we then relate to the Young’s modulus of the material using membrane theory. The presented method is fast, contactless, and provides a platform for high-frequency characterization of the mechanical properties of 2D materials., The mechanical resonances of atomically thin membranes show nonlinear responses at driving forces in the picoNewton range. Here, the authors develop a contactless method to extract the Young’s modulus of 2D materials from the nonlinear dynamic response of these nanomechanical resonators.

We present experimental and theoretical studies of single-molecule conductance through nonplanar fullerocurcuminoid molecular dyads in ambient conditions using the mechanically controllable break junction technique. We show that molecular dyads with bare fullerenes form configurations with conductance features related to different transport channels within the molecules, as identified with filtering and clustering methods. The primary channel corresponds to charge transport through the methylthio-terminated backbone. Additional low-conductance channels involve one backbone side and the fullerene. In fullerenes with four additional equatorial diethyl malonate groups attached to them, the latter transport pathway is blocked. Density functional theory calculations corroborate the experimental observations. In combination with nonequilibrium green functions, the conductance values of the fullerocurcuminoid backbones are found to be similar to those of a planar curcuminoid molecule without a fullerene attached. In the nonplanar fullerocurcuminoid systems, the highest-conductance peak occurs partly through space, compensating for the charge delocalization loss present in the curcuminoid system., Financial support from the European Commission (COST Action MOLSPIN CA15128 and EU RISE (DAFNEOX) project SEP-210165479) is gratefully acknowledged. The work at the University of Chile was supported by Fondecyt Regular Project 1181080 (D.D.), Fondecyt Regular Project 1161775 (M.S.), Fondecyt Regular Project 1170524 (D.A.), and Fondequip EQM140055 and EQM180009 (D.D). Powered@NLHPC: this research was partially supported by the supercomputing infrastructure of the NLHPC (ECM-02). E.R. acknowledges MICIIN for grant PGC2018-093863-B-C21 and the Maria de Maeztu Excellence grant MDM-2017-0767, for the computer resources, technical expertise, and assistance provided by the Barcelona Supercomputing Centre and CSUC and to the Generalitat de Catalunya for an ICREA Academia award and grant 2017SGR1289. H.S.J.v.d.Z. acknowledges support from the Dutch Science foundation (NWO). N.A.-A. thanks MEC for grant MAT2016-77852-C2-1-R, to the Generalitat de Catalunya for the grant 2017SGR1277, and the Severo Ochoa Program for Centers of Excellence in R&D (SEV-2015-0496). This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (grant agreement 724981). L.E. thanks the US National Science Foundation (NSF) for generous support of this work under the CHE-1801317 program. The Robert A. Welch Foundation is also gratefully acknowledged for an endowed chair to L.E. (grant AH-0033).

$${\hbox {SrIrO}}_{3}$$ SrIrO 3 , the three-dimensional member of the Ruddlesden–Popper iridates, is a paramagnetic semimetal characterised by a the delicate interplay between spin–orbit coupling and Coulomb repulsion. In this work, we study the anisotropic magnetoresistance (AMR) of $${\hbox {SrIrO}}_{3}$$ SrIrO 3 thin films, which is closely linked to spin–orbit coupling and probes correlations between electronic transport, magnetic order and orbital states. We show that the low-temperature negative magnetoresistance is anisotropic with respect to the magnetic field orientation, and its angular dependence reveals the appearance of a fourfold symmetric component above a critical magnetic field. We show that this AMR component is of magnetocrystalline origin, and attribute the observed transition to a field-induced magnetic state in $${\hbox {SrIrO}}_{3}$$ SrIrO 3 .

In two-dimensional materials research, oxidation is usually considered as a common source for the degradation of electronic and optoelectronic devices or even device failure. However, in some cases a controlled oxidation can open the possibility to widely tune the band structure of 2D materials. In particular, we demonstrate the controlled oxidation of titanium trisulfide (TiS3), a layered semicon-ductor that has attracted much attention recently thanks to its quasi-1D electronic and optoelectron-ic properties and its direct bandgap of 1.1 eV. Heating TiS3 in air above 300 °C gradually converts it into TiO2, a semiconductor with a wide bandgap of 3.2 eV with applications in photo-electrochemistry and catalysis. In this work, we investigate the controlled thermal oxidation of indi-vidual TiS3 nanoribbons and its influence on the optoelectronic properties of TiS3-based photodetec-tors. We observe a step-wise change in the cut-off wavelength from its pristine value ~1000 nm to 450 nm after subjecting the TiS3 devices to subsequent thermal treatment cycles. Ab-initio and many-body calculations confirm an increase in the bandgap of titanium oxysulfide (TiO2-xSx) when in-creasing the amount of oxygen and reducing the amount of sulfur.

We report on the fabrication and measurements of platinum-self-aligned nanogap devices containing cubed iron (core)/iron oxide (shell) nanoparticles (NPs) with two average different sizes (13 and 17 nm). The nanoparticles are deposited by means of a cluster gun technique. Their trapping across the nanogap is demonstrated by comparing the current vs voltage characteristics (I-Vs) before and after the deposition. At low temperature, the I-Vs can be well fitted to the Korotkov and Nazarov Coulomb blockade model, which captures the coexistence of single-electron tunneling and tunnel barrier suppression upon a bias voltage increase. The measurements thus show that Coulombblockaded devices can be made with a nanoparticle cluster source, which extends the existing possibilities to fabricate such devices to those in which it is very challenging to reduce the usual NP agglomeration given by a solution method., This study was supported by the EU Horizon 2020 research and innovation program under the Marie-Sklodowska-Curie Grant Agreement No. 645658 (DAFNEOX Project), by two FONDECYT REGULAR Grant Nos. 1181080 and 1161775, and by two FONDEQUIP Grant Nos. EQM140055 and EQM180009. We thank the Spanish Ministry of Science, Innovation and Universities (Project Nos. MAT2015-71664-R and RTI2018-099960-B-I00) and the Serbian Ministry of Education, Science and Technological Development (Project No. III45018) for their support. A.P. and Z.K. thank Senzor-INFIZ (Serbia) for the cooperation provided during their respective secondments.

Single-molecule break-junction measurements are intrinsically stochastic in nature, requiring the acquisition of large datasets of “breaking traces” to gain insight into the generic electronic properties of the molecule under study. For example, the most probable conductance value of the molecule is often extracted from the conductance histogram built from these traces. In this letter, we present an unsupervised and reference-free machine learning tool to improve the determination of the conductance of oligo(phenylene ethynylene)dithiol from mechanically controlled break-junction (MCBJ) measurements. Our method allows for the classification of individual breaking traces based on an image recognition technique. Moreover, applying this technique to multiple merged datasets makes it possible to identify common breaking behaviors present across different samples, and therefore to recognize global trends. In particular, we find that the variation in the extracted molecular conductance can be significantly reduced resulting in a more reliable estimation of molecular conductance values from MCBJ datasets. Finally, our approach can be more widely applied to different measurement types which can be converted to two-dimensional images.

The bowl-shaped, 3-fold interlinked porphyrin dimer 2 was obtained in respectable yields during macrocyclization attempts. Its bicyclic structure, consisting of a macrocycle made of a pair of acetylene interlinked tetraphenylporphyrins which are additionally linked by a C-C bond interlinking two pyrrole subunits, has been confirmed spectroscopically (2D-NMR, UV/vis, HR-MALDI-ToF MS). Late-stage functionalization provided the structural analogue 1 with acetyl-protected terminal thiol anchor groups enabling single molecule transport investigations in a mechanically controlled break junction experiment. The formation of single-molecule junctions was observed, displaying large variations in the observed conductance values pointing at a rich diversity in the molecular junctions.

Two-dimensional (2D) materials with strong in-plane anisotropy are of interest for enabling orientation-dependent, frequency-tunable, optomechanical devices. However, black phosphorus (bP), the 2D material with the largest anisotropy to date, is unstable as it degrades in air. In this work we show that As2S3 is an interesting alternative, with a similar anisotropy to bP, while at the same time having a much higher chemical stability. We probe the mechanical and optical anisotropy in As2S3 by three distinct angular-resolved experimental methods: Raman spectroscopy, atomic force microscopy (AFM), and resonance frequency analysis. Using a dedicated angle-resolved AFM force-deflection method, an in-plane anisotropy factor of EaEc=1.7 is found in the Young's modulus of As2S3 with Ea-axis = 79.1 ± 10.1 GPa and Ec-axis = 47.2 ± 7.9 GPa. The high mechanical anisotropy is also shown to cause up to 65% difference in the resonance frequency, depending on crystal orientation and aspect ratio of membranes.

A new concept to improve the reliability of functional single molecule junctions is presented using the E-field triggered switching of FeIIbis-terpyridine complexes in a mechanically controlled break junction experiment as model system. The complexes comprise a push-pull ligand sensing the applied E-field and the resulting distortion of the FeII ligand field is expected to trigger a spin-crossover event reflected in a sudden jump of the transport current. By molecular engineering, the active centre of the complex is separated from the gold electrodes in order to eliminate undesired side-effects. Two aspects are considered to isolate the central metal ion, namely the spacing by introducing additional alkynes, and the steric shielding achieved by bulky isopropyl groups. With this small series of model complexes, a pronounced correlation is observed between the occurrence of bistable junctions and the extent of separation of the central metal ion, affirming the hypothesized Enhanced Separation Concept (ESC).